Servomotors installed in various types of robots work to drive joints of a robot body, and, when the servomotors are off, no braking force acts on them. In an articulated robot, this may result that an arm vertically rotatable by a joint falls by gravity. In a SCARA (Selective Compliance Assembly Robot Arm) robot, this may result that an arm vertically rotatable by a joint moves downward by gravity.
Thus, in order to address the problem, power-off brakes are commonly installed in various types of robots. The power-off brakes are configured to brake at least one servomotor for driving at least one joint affected by gravity in its stopped state.
A power-off brake applies mechanical braking force to a servomotor with a brake-release power source being disconnected thereto, and stops the application of the mechanical braking force to the servomotor with the brake-release power source being connected thereto.
Specifically, during the servomotor being deenergized, the power-off brake is configured to be isolated from the brake-release power source. The servomotor can be turned on with the power-off brake being energized by the brake-release power source.
In order to address emergency situations required to move a robot body in such a state where a servomotor for moving the robot is stopped by mechanical braking force applied from a corresponding power-off brake, a manually operable brake-release on/off button switch is provided on the robot body. The brake-release on/off button switch, referred to simply as “brake-release switch”, is connected between the brake-release power source and the power-off brake.
When switched on, the brake-release switch allows establishment of electrical connection between the brake-release power source and the power-off brake to thereby stop the application of the mechanical braking force to the servomotor.
FIG. 7 schematically illustrates an example of a circuit for controlling the power-off brake in response to on/off operation of the brake-release switch.
Off state of a switch 104 disconnects a brake-release power source 105 from a power-off brake 102 (see FIG. 7) so that the power-off brake 102 works to apply mechanical braking force to a servomotor (not shown) of a robot body 101.
When a brake-release switch 106 provided on the robot body 101 is switched on, electrical connection between the power-off brake 102 and the brake-release power source 105 is established. This prevents the power-off brake from applying the mechanical braking force to the servomotor, allowing the robot body 1 to move.
In articulated robots or the like, when a power-off brake is released, a vertically swingable arm may fall by gravity, or an arm may rise due to air unbalance. In this uncontrolled movement of a link, such as an arm, of the robot body, a dynamic brake of a servomotor associated with the uncontrolled movement of the robot body is activated so that braking force acts on the uncontrolled movement of the link of the robot body. This reduces high-speed movement of the part of the robot body.
However, when the power-off brake is released with the dynamic brake failing, a link of the robot body may start to move at a high speed simultaneously with the release of the power-off brake.
In order to address such a problem, Japanese Patent Application Publication No. H04-315593 discloses a mechanism configured to cause a ratchet to be engaged with an arm vertically movable by a joint of a robot body; this permits the vertically movable arm to only move upward to thereby prevent the vertically movable arm from moving downward.
However, the structure of the mechanism required to cause the ratchet to be engaged with the vertically movable arm of the robot body may increase complexity of the structure of the robot body.